The field of this invention relates generally to video cameras and systems, and more specifically, to a video camera system in which the camera head thereof is powered at least in part by electrical energy converted from optical energy produced by a light source.
In the recent past, the need for small, lightweight video cameras using a solid state image sensor ("imager") such as a charge coupled device ("CCD"), charge injection device ("CID"), or a metal oxide semiconductor ("MOS") device, has rapidly developed for both medical and industrial applications. One medical application involves a video camera attached to an endoscope to allow observation of a surgical site, an internal body structure, or an organ. With a diameter of from 4 to 10 mm., endoscopes are passed into body cavities through small holes to observe structures and perform procedures previously requiring large surgical openings.
In this arrangement, the imager may be contained in a small camera head and attached to the endoscope eyepiece so that the camera head/endoscope combination, or video-endoscope, is lightweight and easily manipulable by a surgeon. A flexible cable connects the camera head to the rest of the camera electronics which are usually included in a camera control unit located remotely from the camera head, and connected via a cable. The camera control unit includes control and video processing circuitry which sends operating signals to the imager and receives signals from the imager which are processed for video display. The camera control unit is also coupled to a video monitor for viewing of the surgical site by one or more physicians. The smallest cameras are made with a single imager but other multiple-imager cameras are also in use, as described in U.S. Pat. No. 5,428,386, which is hereby fully incorporated by reference herein as though set forth in full.
An industrial application employing an imager involves observation of industrial processes in which direct observation by a person is unsafe or otherwise impractical. Such processes include those occurring in nuclear power generating stations, furnaces or engine compartments, or other processes which are generally inaccessible. Here, a camera head including an imager may be attached to a hole in the wall of the vessel in which the process occurs. The camera head is then connected by cable to a camera control unit and video monitor at a remote location in similar fashion to that described above.
Additional background and details regarding video cameras, and their use in medical endoscopic applications, are provided in the following co-pending applications and/or patents, each of which is assigned to Linvatec Corp., and each of which is hereby incorporated by reference herein as though set forth in full:
______________________________________ Filing/ Serial/U.S. Pat No. Issue Date Title ______________________________________ USPN 5,696,553 Issued REMOTE IMAGER December 9, VIDEO CAMERA 1997 CABLE COMPENSATION CIRCUITRY USSN 08/687,086 Filed FIBERSCOPE July 23, 1996 ENHANCEMENT SYSTEM USSN 08/589,875 Filed REMOTE CCD January 23, VIDEO CAMERA 1996 WITH NON- VOLATILE DIGITAL MEMORY USPN 5,587,736 Issued STERILIZABLE CCD December 24, VIDEO CAMERA 1996 USSN 08/606,220 Filed ELECTRICALLY-ISOLATED February 23, STERILIZABLE, ENDOSCOPIC 1996 VIDEO CAMERA HEAD USPN 5,428,386 Issued REMOTE 3D VIDEO CAMERA June 27, 1995 SYSTEM ______________________________________
A critical design goal of an endoscopic CCD video camera is electrical safety, both from the standpoint of the operator, and from the standpoint of the patient. Of particular relevance in this regard is the recently adopted safety requirements and regulations of the unified European Community (EC)--the International Electrotechnical Commission, Medical Equipment Particular Standards for Safety of Endoscopic Equipment (IEC 601-2-18)--which are not only becoming common for all Europe, but are finding acceptance world-wide, including within testing agencies in the United States such as the Underwriters Laboratories (UL) standard UL2601. One specific aspect of these safety regulations states that endoscopic equipment that contacts the patient, and in some cases the operator, must be electrically isolated from ground and power sources.
A problem thus arises because most endoscopic video cameras include a grounded metal housing to (1) protect the sensitive CCD imager and associated electronics from susceptibility to externally generated electromagnetic interference (EMI) and (2) control emissions of electro-magnetic energy generated internally by the camera head circuitry. The need to achieve acceptable electromagnetic compatibility (EMC), that is, to control electromagnetic susceptibility and emissions, is quite important. This is especially true in the surgical setting in which there often exists both strong sources of EMI such as electrocautery units and sensitive instruments such as oxygen and CO.sub.2 monitors.
Moreover, permissible electromagnetic emission levels are now specified by domestic and international regulations in the same way as other safety standards. In Europe, pursuant to International Electrotechnical Commission IEC 601-1-2, the governing standards are defined by CISPR 11, IEC 801-2, IEC 801-3, IEC 801-4, and IEC 801-5; in the United States, the Food and Drug Administration (FDA) has set forth the applicable standard in MDS 201-0004; and in the United European community (EU), according to an EMC Directive, the governing standards are essentially a composite of the above. In current endoscopic video cameras, the metal housing can easily contact the patient or operator, thus interfering with the objective of achieving compliance with applicable domestic and international safety standards.
Another problem is the difficulty of isolating the patient or user from the power sources (typically located in the control unit) used to drive the imager electronics and the camera control unit. Attempts to isolate the camera head from the endoscope by constructing the endoscope eyepiece from a non-metallic material have not proven entirely successful because the limited isolation provided thereby has been easily bridged by the operator's wet hand. Furthermore, there are currently no industry or agency standards that control the eyepiece to coupler attachment so that the amount of isolation at this interface is uncertain.
The problem is even worse in configurations employing one piece video-endoscopes in which the camera head and endoscope are screwed together or permanently joined. Such configurations have recently become more popular as physicians have become more comfortable with the practice of viewing images produced by an endoscope on a television monitor, in contrast to viewing these images directly through the endoscope eyepiece. Such a design eliminates the eyepiece, and with it any possible isolation available therefrom by creating a direct connection between the metal endoscope and the metal camera head housing.
Further, prior attempts to achieve electrical isolation have not proven successful. For example, Kikuchi, U.S. Pat. No. 4,931,867, describes an approach in which the camera control electronics are segregated into a camera input circuit and a camera output circuit which are isolated from one another through isolation circuitry. This approach is not satisfactory because it allows the camera input circuit and cable shield to float relative to the camera output circuit and video output. Consequently, the potential between this circuitry can become large and induce noise into the sensitive camera circuits. Moreover, electrical isolation between the patient and the metal enclosure of the camera head is not achieved.
Another critical design goal of an endoscopic CCD video camera is sterilizability. Because the camera head and cable are used within the sterile field (an arbitrary area around the surgical site) they must be disinfected like other surgical instruments. The steam autoclave method has long been the preferred method for sterilization, especially for instruments that can withstand the necessary high temperature, 134.degree. C., and the extreme conditions associated with steam sterilization. In the past, instruments such as endoscopic cameras were not thought as being able to withstand the steam autoclave process. Accordingly, these instruments were either treated by less effective means such as cold soak processes or moderate temperature (55.degree. C.) processes, or the camera head and cable were covered with a sterile disposable plastic cover during surgery. Each of these methods has significant disadvantages when compared with the steam autoclave method. For example, the cold soak processes do not achieve the same level of sterility, and the moderate temperature processes involve longer cycle times (2 hours) and the handling and disposal of highly toxic chemicals.
Recently, short exposure steam sterilization techniques have been developed to sterilize instruments more rapidly. One such method, known as flash sterilization, reduces the usual steam autoclave time of 45 minutes to less than 10 minutes by using vacuum evacuation of the steam chamber and elimination of the cloth wrapping procedure that protects the sterilized instruments during storage. The appearance of increasingly virulent contaminates and the need to quickly prepare instruments between procedures has made flash steam sterilization the method of choice for many surgical instruments.
The problem is that the camera cable and associated camera head connector are particularly vulnerable to damage from the foregoing cleaning and sterilization processes and historically have been the first to fail in use. Another problem is that the interruption in the integrity of the camera head which is incidental to the need to couple a cable to the camera head with a camera head connector interferes with the objective of providing a camera head which is sufficiently durable and sealed, that it is capable of undergoing the steam autoclave process while providing a waterproof environment to the interior camera head electronics.
A third design goal of a CCD video camera is that it be lightweight and easy for a surgeon to manipulate. The problem is that the camera head cable can be cumbersome and make it more difficult to manipulate the camera head. Although, as disclosed in U.S. Pat. No. 4,633,304, attempts have been made to eliminate the cable by establishing a wireless interface between an insertion section of an endoscope assembly and an operating unit, such efforts have not proven practical because these efforts have included the introduction of a relatively heavy and bulky local power supply such as a battery. A relatively heavy and bulky local power supply such as a battery is problematic because it does not permit easy manipulation of the video camera head, and is susceptible to damage during the steam autoclave sterilization process. Furthermore, the need to monitor and periodically recharge batteries, or interchange them with recharged units, resulting in periodic unsealing of the camera head, contributes to the undesirability of this approach.
A fourth design goal of a CCD video camera is avoiding or reducing interference between externally or internally generated radiation and the camera electronics. The problem is that, as mentioned earlier, a grounded metal housing is sometimes included for this purpose; however, it may interfere with achieving compliance with applicable safety standards. Moreover, the cable linking the camera head to the control unit is a major source of this interfering radiation, but substitution of a wireless communications interface for the cable may necessitate the introduction of a relatively heavy and bulky power supply.
A fifth design goal of a CCD video camera system is repairability. The problem is that the percentage of repairs that are related to cable failures is significant; however, again, the substitution of a wireless communications interface for the cable between the camera head and the control unit may necessitate the introduction of a relatively heavy and bulky power supply.
Consequently, it is an object of the subject invention to provide a video camera head configured for use in an endoscopic video camera system which permits substantial electrical isolation of the patient from power sources and ground. Another objective is to provide a video camera head which is readily sterilizable through the steam autoclave process. A third objective is to provide a video camera head which is lightweight and easy to manipulate. A fourth objective is to provide a wireless interface between the camera head and a corresponding control unit which avoids placement of a power supply within the camera head which is heavy, bulky, or requires periodic maintenance. Further objects of the invention include utilization of the above concepts alone or in combination. Additional advantages and objects will be set forth in the description which follows, or will be apparent to those of ordinary skill in the art who practice the invention.